Abstract

Studying the diet of Antarctic krill (Euphausia superba Dana) is important for modelling theflow of energy and nutrients through the Southern Ocean food web. Previous studies havedemonstrated that krill consume a diverse range of prey, but, have failed to detect or quantifythe contribution of important prey groups. The aim of this thesis was to examine whethernew DNA based methods can contribute to the analysis of krill diet.Initial work developed methods for preserving, extracting and analysing prey DNA derivedfrom krill stomachs. These methods were shown to be capable of preserving large amountsof intact prey DNA and generating reproducible diet data. However, two problems with themethod were identified.The first problem was the presence of a large amount of predator DNA in diet samples thatcompeted with prey DNA during PCR amplification. Further work developed methods thatremoved predator DNA prior to PCR, or, blocked predator DNA amplification during PCR.These methods were successful when applied to a simplified test system but failed whenapplied to real field samples.The second problem was a discrepancy between the results obtained with DNA andconcurrent results obtained with microscopy. This suggested the initial method suffered frombias that skewed results for some prey groups. Subsequent work attempted to resolve thisproblem by changing the approach from quantifying various prey within individual krillstomachs to quantifying the presence or absence of various prey groups in a large numberof krill. When applied to field samples this approach correctly identified the same prey groupsas microscopy, and, suggested that gastropods are a more important component of krill dietthan previously recognised. However, there were still issues regarding the quantification ofprey.The remaining work focused on fundamental issues related to the longevity andquantification of prey DNA in krill stomachs. In krill stomachs, prey DNA was found to: bestable for several hours after ingestion, vary in quantity over six orders of magnitude; and,exit the stomach faster when krill continued to engage in feeding activity. Overall the resultswere promising and the application of DNA methods to krill diet warrants furtherinvestigation.